US4224521A - Microphonics elimination circuit - Google Patents
Microphonics elimination circuit Download PDFInfo
- Publication number
- US4224521A US4224521A US05/950,334 US95033478A US4224521A US 4224521 A US4224521 A US 4224521A US 95033478 A US95033478 A US 95033478A US 4224521 A US4224521 A US 4224521A
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- 230000008030 elimination Effects 0.000 title description 3
- 238000003379 elimination reaction Methods 0.000 title description 3
- 230000000694 effects Effects 0.000 claims abstract description 14
- 238000000034 method Methods 0.000 claims abstract description 9
- 238000001514 detection method Methods 0.000 claims description 5
- 230000005670 electromagnetic radiation Effects 0.000 claims description 2
- 238000012935 Averaging Methods 0.000 claims 1
- 230000005855 radiation Effects 0.000 description 9
- 230000002596 correlated effect Effects 0.000 description 3
- 238000003491 array Methods 0.000 description 2
- 238000010420 art technique Methods 0.000 description 2
- 238000001816 cooling Methods 0.000 description 2
- 238000012986 modification Methods 0.000 description 2
- 230000004048 modification Effects 0.000 description 2
- 230000009467 reduction Effects 0.000 description 2
- 239000000758 substrate Substances 0.000 description 2
- 230000000295 complement effect Effects 0.000 description 1
- 230000000875 corresponding effect Effects 0.000 description 1
- 239000013078 crystal Substances 0.000 description 1
- 230000003247 decreasing effect Effects 0.000 description 1
- 230000006872 improvement Effects 0.000 description 1
- 230000008569 process Effects 0.000 description 1
- 230000004044 response Effects 0.000 description 1
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Classifications
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01J—MEASUREMENT OF INTENSITY, VELOCITY, SPECTRAL CONTENT, POLARISATION, PHASE OR PULSE CHARACTERISTICS OF INFRARED, VISIBLE OR ULTRAVIOLET LIGHT; COLORIMETRY; RADIATION PYROMETRY
- G01J5/00—Radiation pyrometry, e.g. infrared or optical thermometry
- G01J5/10—Radiation pyrometry, e.g. infrared or optical thermometry using electric radiation detectors
- G01J5/34—Radiation pyrometry, e.g. infrared or optical thermometry using electric radiation detectors using capacitors, e.g. pyroelectric capacitors
Definitions
- the present invention is in the field of electromagnetic radiation detection systems. More specifically, the present invention is directed to an improved signal handling technique for use with pyroelectric detectors, in order to reduce the effects of microphonics on the output signal of each detector.
- Infrared radiation detection systems which employ pyroelectric type detector elements, are generally considered to be quite desirable, since they operate at ambient temperatures and do not require cooling. The avoidance or elimination of associated cooling systems is particularly important in most airborne applications, where weight is critical.
- pyroelectric detector elements are susceptible to undesirable noise effects on detected radiation signals. Due to the fact that pyroelectric detectors are piezoelectric crystals, unwanted strains due to vibrations, as well as thermal changes caused by received radiation, may occur. These strains cause unwanted noise signal components to be output from the detector elements and must be filtered out.
- each active (exposed to radiation) pyroelectric detector element is employed in combination with a compensating (shaded from radiation) pyroelectric detector element mounted on a common substrate.
- the active detector element is oriented to be exposed to incoming radiation while the compensating detector is arranged adjacent the active detector, but shielded so as to not be exposed to incoming radiation.
- the active and compensating detectors are initially oppositely polarized by the application of opposite voltages. Thereafter, the active and compensating detectors are connected in parallel so that undesirable signals generated, due to substrate temperature changes, are cancelled.
- Vibrational noise is sought to be decreased by the invention described in U.S. Pat. No. 4,060,729.
- the ambient noises are recognized as being due to both temperature variations and ambient vibrations. Therefore, employing a technique similar to that described above, two detector elements are mounted in an adjacent configuration so that they are exposed to identical temperature and vibrational variations.
- two elements are initially oppositely polarized and then connected in parallel to effect cancellation of the noise signals created by the temperature variations and vibration.
- An alternative embodiment is also shown, wherein the two detecting elements are initially polarized the same and the outputs are electrically connected in series opposition, to effect thermal and vibrational noise cancellation.
- the subject invention is intended to overcome the disadvantages noted in the prior art, while at the same time suppressing the effects of thermal and vibrational noise, as well as reducing the effects of random noise.
- the invention lies in signal handling circuitry employed at the detector stage of an infrared detection system prior to feeding the detection signals into a signal utilizing system, such as would normally be employed to locate, identify, or otherwise process information contained in the detector output signals generated in response to received infrared radiation.
- each element is arranged so as to be exposed to a portion of the field of view.
- the detector elements are arranged in the array so that they are subjected to common ambient temperature variations and vibrations.
- the output signal of each detector element is summed with the output signal of all the other detector elements in that array.
- the summed signal is then averaged and the averaged signal is subtracted from each detector output signal.
- the FIGURE is a schematic of an electronic circuit for carrying out the stated purposes of the invention.
- the invention allows for a high density arrangement of pyroelectric detector elements to be mounted in a compact area and to be operated in a manner that will achieve a cancellation of any microphonics noise components, without the use of complementary (inactive) detector elements.
- the multiple detector elements # 1 , # 2 , # 3 , . . . , # n of a pyroelectric detector array 10 are shown having output lines which are respectively fed to buffer amplifiers 11, 12, 13, . . . , 1n.
- the unmodified signals D 1 , D 2 , D 3 , . . . , D n from the respective buffer amplifiers 11, 12, 13, . . . , 1n are fed to corresponding subtraction circuits 21, 22, 23, . . . , 2n.
- the output of the individual subtraction circuits are then fed to a signal utilization system 30 where they are processed as corrected signals, uncontaminated by microphonics.
- the above-indicated detector signals each contain a random noise signal "RN”, which is uncorrelated from the random noise signals of the other detectors. However, since the detectors are in a common array and are all active, the RMS value ⁇ of random noise signals will be approximately equal. Also, the above-indicated signal values each contain a microphonics signal "M”, which is correlated with that same signal in each of the detectors, since the array 10 is subjected to common vibrational forces. Of course, D 1 indicates, as an example, the true signal "S” which is attributed to the point focused image of the I.R. source.
- the detector output signals are combined in summing circuit 40 as:
- the averaged output signal then appears as:
- the averaged output signal is then subtracted from each individual detector output signal to achieve a final detector output signal D Fi in which the effects of microphonics are eliminated with only a slight increase in the random noise signal and only a slight reduction in the true signal.
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- Engineering & Computer Science (AREA)
- Power Engineering (AREA)
- Physics & Mathematics (AREA)
- General Physics & Mathematics (AREA)
- Spectroscopy & Molecular Physics (AREA)
- Photometry And Measurement Of Optical Pulse Characteristics (AREA)
- Radiation Pyrometers (AREA)
Abstract
The effects of microphonic noise on the output of an array of commonly-mounted pyroelectric detectors are suppressed by contemporaneously adding the signal outputs from all of the detectors, determining the averaged signal, and separately subtracting the averaged signal from each detector output. The method cancels microphonic noise and reduces random noise with only a slight decrease in the signal-to-noise ratio.
Description
1. Field of the Invention
The present invention is in the field of electromagnetic radiation detection systems. More specifically, the present invention is directed to an improved signal handling technique for use with pyroelectric detectors, in order to reduce the effects of microphonics on the output signal of each detector.
2. Description of the Prior Art
Infrared radiation detection systems, which employ pyroelectric type detector elements, are generally considered to be quite desirable, since they operate at ambient temperatures and do not require cooling. The avoidance or elimination of associated cooling systems is particularly important in most airborne applications, where weight is critical. However, it is recognized that pyroelectric detector elements are susceptible to undesirable noise effects on detected radiation signals. Due to the fact that pyroelectric detectors are piezoelectric crystals, unwanted strains due to vibrations, as well as thermal changes caused by received radiation, may occur. These strains cause unwanted noise signal components to be output from the detector elements and must be filtered out.
An example of a prior art attempt to eliminate unwanted signal components is shown in U.S. Pat. No. 3,453,432. In that patent, each active (exposed to radiation) pyroelectric detector element is employed in combination with a compensating (shaded from radiation) pyroelectric detector element mounted on a common substrate. The active detector element is oriented to be exposed to incoming radiation while the compensating detector is arranged adjacent the active detector, but shielded so as to not be exposed to incoming radiation. The active and compensating detectors are initially oppositely polarized by the application of opposite voltages. Thereafter, the active and compensating detectors are connected in parallel so that undesirable signals generated, due to substrate temperature changes, are cancelled.
Vibrational noise is sought to be decreased by the invention described in U.S. Pat. No. 4,060,729. In this patent, the ambient noises are recognized as being due to both temperature variations and ambient vibrations. Therefore, employing a technique similar to that described above, two detector elements are mounted in an adjacent configuration so that they are exposed to identical temperature and vibrational variations. In a first embodiment, two elements are initially oppositely polarized and then connected in parallel to effect cancellation of the noise signals created by the temperature variations and vibration. An alternative embodiment is also shown, wherein the two detecting elements are initially polarized the same and the outputs are electrically connected in series opposition, to effect thermal and vibrational noise cancellation.
While the above prior art techniques are suitable for some applications, it has been found that most lightweight, compact, airborne design applications do not allow the luxury of redundant compensation detectors in an array of active pyroelectric detectors. In addition, it has also been found that the above discussed prior art techniques, while reducing noise due to thermal and vibrational variation, produce an increase in random noise signal power. This is due to the fact that uncorrelated random noise is generated independently in each separate pyroelectric detector element. Therefore, when the outputs of two detector elements are subtracted, the random noise power is doubled, rather than cancelled.
The subject invention is intended to overcome the disadvantages noted in the prior art, while at the same time suppressing the effects of thermal and vibrational noise, as well as reducing the effects of random noise. The invention lies in signal handling circuitry employed at the detector stage of an infrared detection system prior to feeding the detection signals into a signal utilizing system, such as would normally be employed to locate, identify, or otherwise process information contained in the detector output signals generated in response to received infrared radiation.
In an array of "active" pyroelectric detector elements, each element is arranged so as to be exposed to a portion of the field of view. The detector elements are arranged in the array so that they are subjected to common ambient temperature variations and vibrations. The output signal of each detector element is summed with the output signal of all the other detector elements in that array. The summed signal is then averaged and the averaged signal is subtracted from each detector output signal. This technique serves to cancel out the correlated microphonic noise effects caused by vibrational forces in each of the elements as well as by ambient temperature variations, which commonly effect the detector elements. This technique achieves the cancellation of the microphonics with only a slight decrease in the signal to noise ratio characteristics.
It is therefore a purpose of the invention to provide an improved signal handling technique for reducing microphonic effects in pyroelectric detector arrays.
It is another object of the invention to provide circuitry for carrying out the above described technique.
It is a further object of the present invention to increase active element densities in pyroelectric detector arrays while eliminating microphonic effects on the individual output signals from the array.
The FIGURE is a schematic of an electronic circuit for carrying out the stated purposes of the invention.
The invention, as summarized above, allows for a high density arrangement of pyroelectric detector elements to be mounted in a compact area and to be operated in a manner that will achieve a cancellation of any microphonics noise components, without the use of complementary (inactive) detector elements.
By referring to the accompanying FIGURE, the invention will be described in detail. The multiple detector elements #1, #2, #3, . . . , #n of a pyroelectric detector array 10 are shown having output lines which are respectively fed to buffer amplifiers 11, 12, 13, . . . , 1n. The unmodified signals D1, D2, D3, . . . , Dn from the respective buffer amplifiers 11, 12, 13, . . . , 1n are fed to corresponding subtraction circuits 21, 22, 23, . . . , 2n. The output of the individual subtraction circuits are then fed to a signal utilization system 30 where they are processed as corrected signals, uncontaminated by microphonics.
Therefore, assuming a detector array 10 employing, for example, 100 detector elements (n=100), wherein one detector, such as "#1", receives a point focus of infrared radiation, the signals output from respective buffer amplifiers are as follows:
______________________________________ D.sub.1 = S + RN.sub.1 + M D.sub.2 = RN.sub.2 + M D.sub.3 = RN.sub.3 + M . . . . . . . . . . . . D.sub.100 = RN.sub.100 + M ______________________________________
The above-indicated detector signals each contain a random noise signal "RN", which is uncorrelated from the random noise signals of the other detectors. However, since the detectors are in a common array and are all active, the RMS value σ of random noise signals will be approximately equal. Also, the above-indicated signal values each contain a microphonics signal "M", which is correlated with that same signal in each of the detectors, since the array 10 is subjected to common vibrational forces. Of course, D1 indicates, as an example, the true signal "S" which is attributed to the point focused image of the I.R. source.
The detector output signals are combined in summing circuit 40 as:
D.sub.1 +D.sub.2 +D.sub.3 . . . +D.sub.100
The summed signal is then averaged by the known number of detectors (n=100) in the array at divider 42. The averaged output signal then appears as:
[S+RN.sub.1 +(RN.sub.2 +RN.sub.3 + . . . RN.sub.n)+nM]/n
The averaged output signal is then subtracted from each individual detector output signal to achieve a final detector output signal DFi in which the effects of microphonics are eliminated with only a slight increase in the random noise signal and only a slight reduction in the true signal.
For the exemplified detector D1, the final output signal appears as:
D.sub.F1 =[S+RN.sub.1 +M]-[S+RN.sub.1 +nM+RN.sub.2 +RN.sub.3 + . . . +RN.sub.n ]/n.
Correlated microphonics cancel and the expression reduces to: ##EQU1## Since the expression RN2 +RN3 + . . . +RNn contains n-1 terms, this reduces to an RMS value of random noise ##EQU2## Therefore, the true signal component S of the final detector output signal for D1 is reduced by s/n and becomes ##EQU3## e.g., for n=100, S is reduced by 1%. The signal to RMS random noise voltage ratio is also reduced by a factor of ##EQU4## and becomes ##EQU5##
It is therefore clear, by the above description, that although some reduction is made in the true signal component and the signal to noise ratio, the present invention contributes an improvement to the art by providing an elimination of microphonics noise effects in a compact array of active detectors. It is further apparent that many modifications and variations may be made to the invention without departing from the scope fo the novel concept of this invention. Therefore, it is intended by the appended claims to cover all such modifications and variations which fall within the true spirit and scope of the invention.
Claims (2)
1. In an electromagnetic detection system including an array of "n" commonly mounted pyroelectric detectors, where "n" is a whole number greater than 1 and said pyroelectric detectors are sensitive to electromagnetic radiation to produce respective output signals, and a circuit for reducing signal effects of microphonics generated by said detectors, said circuit comprising:
means for contemporaneously adding the signal outputs from "n" detectors and producing a summing signal;
means for averaging said summing signal by a factor of 1/n and generating an average signal;
means for separately subtracting said averaged signal from each of said signal outputs to cancel correlative signal components and produce corresponding output signals without microphonics.
2. A method of processing signals output from a commonly mounted array of like pyroelectric detectors to eliminate correlative signal components, such as mirophonics, including the steps of:
summing the pyroelectric detector output signals;
dividing said summed signal by the number of detectors to produce an averaged signal; and
subtracting the averaged signal for each detector output signal to produce a correspondingly corrected output signal for each detector.
Priority Applications (1)
Application Number | Priority Date | Filing Date | Title |
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US05/950,334 US4224521A (en) | 1978-10-11 | 1978-10-11 | Microphonics elimination circuit |
Applications Claiming Priority (1)
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US05/950,334 US4224521A (en) | 1978-10-11 | 1978-10-11 | Microphonics elimination circuit |
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US4224521A true US4224521A (en) | 1980-09-23 |
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US05/950,334 Expired - Lifetime US4224521A (en) | 1978-10-11 | 1978-10-11 | Microphonics elimination circuit |
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Cited By (3)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
US6114698A (en) * | 1997-01-31 | 2000-09-05 | The United States Of America As Represented By The Secretary Of Commerce | Domain engineered ferroelectric optical radiation detector |
US6630671B2 (en) | 1997-01-31 | 2003-10-07 | The United States Of America As Represented By The Secretary Of Commerce | Domain engineered ferroelectric optical radiation detector having multiple domain regions for acoustic dampening |
WO2014210438A3 (en) * | 2013-06-27 | 2015-06-04 | The Regents Of The University Of California | Active microphonic noise cancellation in radiation detectors |
Citations (9)
Publication number | Priority date | Publication date | Assignee | Title |
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US3398285A (en) * | 1961-10-16 | 1968-08-20 | Perkin Elmer Corp | Spectro-radiometer with means for eliminating background noise |
US3453432A (en) * | 1966-06-23 | 1969-07-01 | Barnes Eng Co | Pyroelectric radiation detector providing compensation for environmental temperature changes |
US3531802A (en) * | 1968-09-16 | 1970-09-29 | Presearch Inc | Cumulative enhancement signal processor |
US3732420A (en) * | 1971-06-25 | 1973-05-08 | Picker Corp | Automatic calibration system for a scintillation device |
US3787668A (en) * | 1973-02-22 | 1974-01-22 | Us Army | Adaptive threshold unit |
US3806729A (en) * | 1973-04-30 | 1974-04-23 | Texas Instruments Inc | Charge coupled device ir imager |
US3916325A (en) * | 1963-10-31 | 1975-10-28 | Bell Telephone Labor Inc | Antenna side lobe rejection system |
US4039883A (en) * | 1972-07-04 | 1977-08-02 | U.S. Philips Corporation | Soldered joint |
US4060729A (en) * | 1976-12-10 | 1977-11-29 | Martin Marietta Corporation | Pyroelectric detector with decreased susceptibility to vibrational noise |
-
1978
- 1978-10-11 US US05/950,334 patent/US4224521A/en not_active Expired - Lifetime
Patent Citations (9)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
US3398285A (en) * | 1961-10-16 | 1968-08-20 | Perkin Elmer Corp | Spectro-radiometer with means for eliminating background noise |
US3916325A (en) * | 1963-10-31 | 1975-10-28 | Bell Telephone Labor Inc | Antenna side lobe rejection system |
US3453432A (en) * | 1966-06-23 | 1969-07-01 | Barnes Eng Co | Pyroelectric radiation detector providing compensation for environmental temperature changes |
US3531802A (en) * | 1968-09-16 | 1970-09-29 | Presearch Inc | Cumulative enhancement signal processor |
US3732420A (en) * | 1971-06-25 | 1973-05-08 | Picker Corp | Automatic calibration system for a scintillation device |
US4039883A (en) * | 1972-07-04 | 1977-08-02 | U.S. Philips Corporation | Soldered joint |
US3787668A (en) * | 1973-02-22 | 1974-01-22 | Us Army | Adaptive threshold unit |
US3806729A (en) * | 1973-04-30 | 1974-04-23 | Texas Instruments Inc | Charge coupled device ir imager |
US4060729A (en) * | 1976-12-10 | 1977-11-29 | Martin Marietta Corporation | Pyroelectric detector with decreased susceptibility to vibrational noise |
Cited By (4)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
US6114698A (en) * | 1997-01-31 | 2000-09-05 | The United States Of America As Represented By The Secretary Of Commerce | Domain engineered ferroelectric optical radiation detector |
US6630671B2 (en) | 1997-01-31 | 2003-10-07 | The United States Of America As Represented By The Secretary Of Commerce | Domain engineered ferroelectric optical radiation detector having multiple domain regions for acoustic dampening |
WO2014210438A3 (en) * | 2013-06-27 | 2015-06-04 | The Regents Of The University Of California | Active microphonic noise cancellation in radiation detectors |
US10126443B2 (en) | 2013-06-27 | 2018-11-13 | The Regents Of The University Of California | Active microphonic noise cancellation in radiation detectors |
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AS | Assignment |
Owner name: LORAL AEROSPACE CORP. A CORPORATION OF DE, NEW Y Free format text: ASSIGNMENT OF ASSIGNORS INTEREST.;ASSIGNOR:FORD AEROSPACE CORPORATION, A DE CORPORATION;REEL/FRAME:005906/0022 Effective date: 19910215 |